A wire saw using a fixed abrasive wire is one example of an apparatus which is configured to run lines of fine wire imparted with tension, press an object to be cut (for example, silicon ingot) against the lines of wire while spraying a slurry of abrasive material containing abrasives to the lines of wire, and cut the object into wafers by utilizing the grinding properties of loose abrasives. Since this apparatus is capable of obtaining plural wafers at a time, the process making use of the apparatus is called a multicutting method. FIG. 14 is an example of a schematic illustration of the construction of a wire saw apparatus for use in machining single-crystalline silicon.
Referring briefly to FIG. 14, wire 42 fed from a feed bobbin 41 passes through many guide rollers 43 arranged to guide the wire and then forms lines of wire with predetermined intervals at plural groove rollers 44 each having many grooves. A feed unit 45 presses an object 46 to be cut against the lines of wire, while a slurry of loose abrasives is sprayed on the lines of wire from nozzle 47, whereby the object 46 is cut into wafers. Thereafter, the lines of wire are passed through many guide rollers 48 and then taken up by a take-up bobbin 49. The wire 42 is driven by the driving power of a drive motor 50 associated with the groove rollers 44. During running of the wire 42, data about movements of dancer rollers 51 and 52 is fed back to rotation of each of the feed bobbin 41 and take-up bobbin 49 to maintain the tension of the wire 42 constant. Usually, the wire 42 advances with bidirectional or unidirectional run to meet requests for effective utilization of the wire 42 as a material and improvements in the quality of the resulting products such as improvement in cut surface roughness and is finally taken up by the take-up bobbin 49.
Generally, a dispersion of abrasives of silicon carbide in a lubricant is often used as the above slurry of loose abrasives. Such a lubricant is usually a mineral oil. However, such a mineral oil lubricant requires an organic solvent for cleaining, which raises an environmental problem and, for this reason, a change for a water-soluble lubricant based on a glycol-type solvent is now under way. Such a wire saw using loose abrasives is characterized in that: (1) since the wire saw is of the type configured to cut the whole of an object to be cut at a stroke, the wire saw is capable of handling large amounts of objects even though its cutting speed is not high; (2) since the cutting tool is wire, an object to be cut having a large bore diameter can be cut relatively easily; and (3) since cutting is achieved relying upon the grinding properties of loose abrasives while using a fine wire as the cutting tool, the object can be cut into thin wafers. On the other side, the wire saw has such drawbacks that: the use of a slurry of loose abrasives causes the abrasives to scatter on the workbench, thereby contaminating the working environment due to dryness of the abrasives; and disposal of waste and cleaning of wafers are required.
As means for eliminating these drawbacks, a fixed abrasive wire has been proposed which is made by attaching diamond abrasives or the like to a wire by means of a thermosetting or photosetting resin binder and then allowing the resin to thermoset or photoset thereby to fix the abrasives to the wire. However, because the fixing or bonding strength obtained by the method of attaching abrasives to the wire by such a resin is not sufficient, there is fear that the abrasives fall off due to friction caused by cuffing during the process of cutting the object into wafers by intense reciprocation of the wire.
In attempt to solve the above problems associated with the wire saw using loose abrasives and the wire saw obtained by attachment of abrasives to the wire by means of resin, patent documents 1 to 3 have proposed abrasive electrodeposited wire saws of the type in which abrasives are fixed on a wire by an electrolytic process.
Patent document 1 discloses a diamond electrodeposited wire or ribbon having a first electrodeposited layer 63 comprising coarse diamond abrasives 62 electrodeposited on a wire or ribbon 61, and a second electrodeposited layer 65 comprising electrodeposited diamond abrasives 64 which are considerably finer than the abrasives 62, in which the second electrodeposited layer 65 is put on the first electrodeposited layer 63, as shown in FIG. 15.
Patent document 2 discloses an abrasive coated wire having an electroplated layer 73 for allowing abrasives 72 to be implanted to the surface of a wire 71, and an electroless-plated layer 74 formed on the outer side of the electroplated layer 73 for reinforcing the implanted condition of the abrasives 72, as shown in FIG. 16.
Patent document 3 discloses a wire saw comprising a coating of a soft plated layer 82 on the surface of a wire 81, and a coating of a hard plated layer 83 on the soft plated layer 82, the two plated layers fixing superabrasives 84 on the wire 81, wherein an inner end 85 of the superabrasives 84 is within the soft plated layer 82 while an outer end 86 of the superabrasives 84 is exposed from the hard plated layer 83 and situated on the same cylindrical surface, as shown in FIG. 17.    Patent document 1: Japanese Patent Provisional Publication No. SHO 63-22275    Patent document 2: Japanese Patent Provisional Publication No. HEI 9-1455    Patent document 3: Japanese Patent Provisional Publication No. HEI 9-150314